The applicants propose a non-radioactive magnetic tracer system to track an oral drug formulation through the digestive tract, and determine the site at which it dissolves. The dosage form is labeled with an inert magnetic material. An array of magnetic sensors measures its magnetic field, and determines its location as a function of time. The dosage form's disintegration is marked by decrease in its magnetic moment. The proposed system, using inexpensive sensor technology, will achieve tracking errors of several mm, with a small amount of magnetic taggant that does not perturb the behavior of the dosage form. The R21 program will (1) test how much taggant can be used without perturbing the dosage form, (2) verify that the sensor system can track that much taggant with adequate accuracy, (3) observe the dissolution of dosage forms in vitro and (4) validate the magnetic tracking in vivo, using x-rays and scintigraphy. This system will be cheaper and more widely available than existing radioscintigraphy methods, and will be applicable to children, pregnant women and elderly subjects. These capabilities will have wide applications in the validation of colonic and enteric drug delivery systems, as well as the diagnosis of gastrointestinal motility disorders.